1. Field of the Invention
The present invention relates to a radar apparatus that detects the distance to and the shape of an obstacle or a preceding car present around a vehicle by employing a two-dimensional scanner.
2. Description of the Related Art
A two-dimensional scanner such as the micro-scanner disclosed in Japanese Laid-Open Patent Publication No. H 9-101474 is employed in a radar apparatus in the related art. Since the mirror of the scanner is driven in response to a sine wave signal when such a two-dimensional scanner is utilized, a sinusoidal Lissajous scanning is performed instead of a linear raster scanning. The results of a scanning operation performed through Lissajous scanning are presented in FIGS. 26 and 27.
As illustrated in FIG. 26, the measurement points within an area scanned through Lissajous scanning may not always be distributed uniformly, i.e., there may be an area over which measurement points are set sparsely and an area where measurement points are set densely, depending upon the relationship between the longitudinal oscillation frequency and the lateral oscillation frequency at which the scanner is caused to oscillate. Since the area where the measurement points are sparse does not remain unchanged and moves within the scanning area as the phases of the wavelengths of the longitudinal oscillation and the lateral oscillation change, the adoption of the Lissajous scan in a radar apparatus (range finder apparatus), which is required to provide consistent measurement results, has been considered problematic. In addition, depending upon the relationship between the longitudinal oscillation frequency and the lateral oscillation frequency, a standing wave may be generated, as shown in FIG. 27. In such a case, the area over which the measurement points are set sparsely expands if the frequency of the standing wave is low, resulting in a problem in that the area where the measurement can be performed becomes smaller.
An object of the present invention is to provide a radar apparatus that does not allow formation of an area where measurement points are sparse within the scanning area and thus is capable of performing a uniform observation of the scanning area by controlling a longitudinal oscillation signal and a lateral oscillation signal in correspondence to the length of time over which the scanning observation is performed.
The radar apparatus according to the present invention comprises a signal transmitter device that transmits a signal, a scanner that two-dimensionally scans a target object using the signal transmitted from the signal transmitter device by engaging in longitudinal oscillation and lateral oscillation, a signal receiver device that receives a reflection signal which is originally transmitted via the scanner and a control device that controls a longitudinal oscillation signal and a lateral oscillation signal used to oscillate the scanner longitudinally and laterally in correspondence to the length of time over which a scanning observation is performed through two-dimensional scanning.